-1- System Software Research Lab. Active Cache : Caching Dynamic Contents on the Web Pei Cao, Jin Zhang and Kevin Beach Middleware’ SSLAB, EE Dept, KAIST 박상호 Comment: 서버 쪽에서 해야할 일들을 proxy 로 이동시키는 방법에 대한 논문. 아이디어가 기발한 것 같진 않지만, 사용 가능한 application 을 찾아 명시하였고, 자바를 이용한 방법을 제시하였다.

-2- System Software Research Lab. Content ▣ Introduction ▣ Active cache protocol ▣ Security Mechanism ▣ Resource Management Policy ▣ Implementation ▣ Performance ▣ Conclusion and critique

-3- System Software Research Lab. Introduction ▣ Caching in the Web ◈ Inability to cache dynamic documents ▣ Active cache ◈ Migrates parts of server processing to the caching proxy ◈ Cache applet : server-supplied code written in JAVA Server Proxy request reply processing Server Proxy processing request reply

-4- System Software Research Lab. Active cache protocol(1/2) ◈ New entity header : CacheApplet –CacheApplet: code=“code.class”, archive=“code.jar”, codebase=“codebase_url” ◈ Active-Cache enabled proxy –Applet’s execution failure : the request is sent to the server –Applet’s execution success : send the cached document or new document to the client –Send the log object back to the server periodically Server/test.html test.html -> test.class Server/test.html With CacheApplet entity header

-5- System Software Research Lab. Active cache protocol(2/2) ▣ Active cache interface Cache hit FromCache() 1:new content 0:cached content -1:forward the request to server ActiveProxy class : File access, cache query, Lock/unlock, sending requests to servers Available : java.util, java.text, java.math, java.security, java.sql, ActiveProxy class Unvailable : java.io, java.lang, java.systems Proxy : CacheApplet :

-6- System Software Research Lab. Cache Applet Examples(1/2) ▣ Logging User Accesses public static int FromCache( string User_HTTP_Request, string Client_IP_Address, string Client_Name, int Cache_File, int New_File) { int fd = open(“logapplet.log”, APPEND_ONLY); int status = lock(fd); string date = new curtime(); log_to_file(fd, date, Client_Name, User_HTTP_Request, Client_IP_Address); status = unlock(fd); close(fd); return(0); // 0 means use the cached file }

-7- System Software Research Lab. Cache Applet Examples(2/2) ▣ Advertising Banner Rotation ▣ Access Permission Checking ▣ Client-Specific Information Distribution ▣ Server-Side Include Expansion ▣ Delta Compression

-8- System Software Research Lab. Security Mechanisms ▣ Two types of security attacks ◈ An applet’s illegal access to information belonging to other web server –JAVA : built-in security mechanism –Applets from different servers do not cooperate –Static examination of the classes and functions ◈ Denial-of-service attacks : resource consumption –Storage size –Disk bandwidth –Network bandwidth –CPU usage –Virtual memory size

-9- System Software Research Lab. Resource Management Policies ▣ Proxy decide whether an object should be cached ◈ Based on the proxy’s estimation of the benefits and the cost of caching –Benefit : saved network bandwidth –Cost : storage cost, CPU cost, network communication(send_request_to_server calls) ◈ Cost-aware cache replacement algorithm ◈ Negotiated object : server specifies the estimated costs and desired duration of caching ◈ Un-negotiated object

-10- System Software Research Lab. Implementation ▣ Implementation ◈ CERN httpd proxy –CacheApplet header –Invoke the applet ◈ setrlimit() system call ◈ Sending the log object : HTTP POST

-11- System Software Research Lab. Performance(1/2) ▣ Applet overhead ◈ WebStone 2.0 ◈ 6 applets : null, log, ads, apc, ssi, clid ◈ Server(SPARC 20), proxy(99MHz Intel x86) Proxy1 client10 clients20 clients null log ads apc ssi csid Response time(active cache) Response time(the original CERN httpd proxy)

-12- System Software Research Lab. Performance(2/2) ▣ Internet traffic reduction through active cache ◈ AT&T WorldNet Internet Service Provider –30% of all user request carry cookies –AT&T traces –35% hit ratios and 30% byte hit ratios –Active cache : 55% hit ratios and 41% byte hit ratios

-13- System Software Research Lab. Conclusion and critique ▣ Conclusion ◈ Support caching of dynamic documents on the Web ◈ Protocol design, interface, security mechanism and resource management strategies ▣ Critique ◈ Bad performance –Increase the number of web server instead of using proxy ◈ Difficult to program –Servlet or jsp ◈ Cache applet restriction